1. Field of the Invention
The present invention relates to a method of communication suitable for use in, for example, a base station and a terminal apparatus in a radio telephone system, and a transmission apparatus and a reception apparatus to which the method of communication is applied.
2. Description of the Related Art
In a mobile communication such as a radio telephone system or the like, multiple access is provided in which a plurality of base stations are provided at a predetermined interval to form a service area and each of the base stations is connected to a plurality of mobile stations (terminal apparatus). In this case, a predetermined transmission band is allocated in advance to each base station; a plurality of transmission channels are set in the transmission band; in the case of a request for communication or the like from each terminal apparatus, any of the transmission channels is allocated to the terminal apparatus; and the terminal apparatus side initiates communication by way of the base station using the allocated transmission channel.
For example, such systems of communication wherein the transmission channels are set include a frequency division multiple access (FDMA), a time division multiple access (TDMA), a code division multiple access (CDMA) and so on.
Referring to each method, the communication system of FDMA system is one in which a plurality of transmission channels are provided by dividing the transmission band prepared by a unit of frequency. The communication system of TDMA system is one in which a transmission channel is divided by a predetermined time unit to form a plurality of time slots within a single transmission channel, each of the time slots being allocated to the terminal equipments to be linked. Therefore, it is possible to link the plurality of terminal equipment using the single transmission channel. The communication system of CDMA system is one in which a specified code is allocated to each of the terminal equipments and a carrier having the same frequency is subjected to spectrum spread modulation by the code for transmitting it to the base station. The receiving side achieves synchronization with each code to identify a signal from a desired terminal apparatus.
In a radio telephone system, even if any of the above systems is employed and a transmission channel is set in accordance therewith, a transmission capacity of data which can be transmitted on one transmission channel is previously determined and hence the transmission capacity cannot be changed depending upon the kink of transmission data. In a general radio telephone system, the transmission capacity of one transmission channel is set so as to be a capacity which allows transmission of audio data for speech.
Recently, while attempt to transmit various data other than audio data by using a radio terminal such as a portable telephone or the like has been made, such a limitation that data of only a predetermined transmission capacity can be transmitted on one transmission channel brings the disadvantage that it takes considerable time to transmit data of a large capacity. In order to solve this problem, it may be sufficient to set a large transmission capacity as the transmission capacity of data which can be transmitted on one channel. However, as the transmission capacity of one channel is increased, a frequency band width of one transmission channel and so on must be set wide to that extent, which consequently reduces the number of transmission channels set in a transmission band allocated to one base station. Moreover, if the data of a comparatively small capacity such as the audio data is transmitted, the data amount to be transmitted on each of transmission channels becomes smaller as compared with the transmission capacity of the transmission channel, which disadvantageously causes an ineffective use of the transmission band.
In order to overcome the above disadvantage, the assignee of this application has proposed a communication method and a communication apparatus to which a transmission system permitting a transmission capacity to be changed is applied (in Japanese patent applications No. 8-312295 and so on). In the above proposed communication system and apparatus, when digital data is transmitted by wireless, an interleaving processing for changing a data arrangement of transmission data is carried out and hence even if a part of data lack upon reception, then it is possible to restore the data by an error correction processing and so on.
Since the above interleaving processing is carried out on condition that data of a predetermined transmission capacity is interleaved, if the above interleaving processing is applied to a communication system with a variable transmission capacity as it is, then a processing for precisely restoring the interleaved data arrangement to its original data arrangement may be disabled on the reception side when the transmission capacity is changed.